Objectives: a. To determine the amino acid sequences of the phosphopeptides, derived from tryptic digestion of the phosphorylated hexokinase isoenzymes.b. To determine whether phosphorylation of the yeast hexokinases by yeast protein kinase may result in regulation of hexokinase activity. c. To determine whether the association of ATP- ADP exchange activity with hexokinase activity involves a specific chemical complex, and whether this association may have physiological significance. d. To select additional hexokinase- deficient yeasts, to characterize more extensively the hexose requirements of each, and to identify the hexokinases in the mutants by immunological as well as chemical means.